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Model Forum / General / Rockets / May 2009New Aerotech RMS-24/60 & air starting motors
Forgive my naive questions, but (geez, I feel like a newbie all over again :) ... I see Aerotech has a new RMS system, the 24/60 and a vendor is offering 40% off the hardware until the end of the month ($45 instead of $75 - which makes it very tempting). Unfortunately, I see on Aerotech's site that they only offer one reload for it: an F35-xW (x = 5, 8 or 11). That makes it not-so-tempting. Does anyone know if the reloads intended for the RMS-24/40 can be used in the 24/60 hardware? Also, how do the high power folk manage to air start motors? Are there electronics that can detect booster stage burnout? One of the projects I've always wanted to do is a functional 2-stage Nike-Apache model rocket (not HPR). Unfortunately, the traditional staging mechanism of using the booster's ejection charge to light the upper stage wouldn't work for such a model. I need to find an alternative for lighting the upper stage. Thanks. > Forgive my naive questions, but (geez, I feel like a newbie all over > again :) ... [quoted text clipped - 13 lines] > stage wouldn't work for such a model. I need to find an alternative > for lighting the upper stage. Yes, you have to come up with some way of firing an igniter. How this is done varies according to how much sophistication and safety people want; a popular technique is to use a mercury switch as an accelerometer; of course, this may ignite really early if the first stage chuffs. So it ought to be combined with a way of detecting you've cleared the launch rod... >> Also, how do the high power folk manage to air start motors? Are >> there electronics that can detect booster stage burnout? One of the [quoted text clipped - 10 lines] >stage chuffs. So it ought to be combined with a way of detecting >you've cleared the launch rod... As Joe indicates, mercury switches do work...sometimes. They're no longer allowed for high-power rockets, partly because of that "sometimes." Likewise for pull-switches, roller switches, and similar methods. One company---can't recall who---used to sell a simple one-chip timer for about $20. Someone who knows electronics better than me can probably construct such a circuit for a buck or less, literally. Set the timer for a half-second longer than the booster burn. Add a "G-switch" (a nickel or a small slug of lead glued to the top of a touch-switch) to start the timer, and a 12-V garage-remote battery to fire an ematch. There are lots of altimeter/timers on the market, more expensive but more reliable than what I've described above. Best -- Terry >>Yes, you have to come up with some way of firing an igniter. How this >>is done varies according to how much sophistication and safety people [quoted text clipped - 7 lines] > "sometimes." Likewise for pull-switches, roller switches, and similar > methods. Thanks -- I wasn't aware they were no longer allowed. > One company---can't recall who---used to sell a simple one-chip timer > for about $20. Someone who knows electronics better than me can [quoted text clipped - 5 lines] > > Best -- Terry What about solid state accelerometers? It seems that electronics that lit the upper stage when it detected booster burnout would be better than guessing with a timing device. Methinks it would be more reliable, too - and not too expensive. (Solid state accelerometers can be found for less than $10). I'm kind of surprised there isn't already something like this out there. >> One company---can't recall who---used to sell a simple one-chip timer >> for about $20. Someone who knows electronics better than me can [quoted text clipped - 12 lines] >can be found for less than $10). I'm kind of surprised there isn't >already something like this out there. Already out there in several flavors. I have one (the G-Wiz). But just as a useable-by-the-beginner timer circuit costs 10X the price of the chip, a useable and proven-reliable accelerometer for rocketry runs around $100-200. I discovered a long time ago that it was far cheaper to purchase a proven design than to attempt to construct my own, with many trials and errors. Mostly errors. Best -- Terry Captain, My preferred timer is the miniTimer3 from PerfectFlite. It's about 40 bucks. http://68.178.208.82/cgi/PF_Store/perlshop.cgi?ACTION=enter&thispage=miniT3.html &ORDER_ID=!ORDERID! You can build a rudimentary timer for the aforementioned dollar or so. It will cover most of the primary staging functions. But it won't handle any anomalies; it won't handle any exceptions. If you trip on your way to the pad, or fart at the wrong instant, or the booster motor chuffs, the upper stage is gonna light at a most inopportune moment. So spend the extra 39 bucks and get a timer that's got some robustness. The miniTimer3 has a good liftoff detect mechanism. A sustained 2G of thrust for 1/2 second must occur before triggering. A user programmable delay can extend that for however long is necessary. (Can't recall the upper limit.) It's not gonna blow up in your face. BTW, you sense booster liftoff, not burnout, with this timer. You set the delay to include the length of booster burn plus any coast time you might want to add. BTW2, if you want to do a "functional 2-stage Nike-Apache model rocket (not HPR)", it's possible to use gap staging. Black powder model rockets can readily stage over a gap of up to a foot. The only issue in this case is recovering the booster. It's complex and iffy getting any sort of chute or streamer deployed off a booster motor. And the traditional tumble recovery won't work; the booster is stable and would lawn dart in. So the timer is probably still the better solution. Doug > On Tue, 28 Apr 2009 08:31:33 -0700 (PDT), Captain > [quoted text clipped - 26 lines] > > Best -- Terry > As Joe indicates, mercury switches do work...sometimes. They're no > longer allowed for high-power rockets, partly because of that > "sometimes." Likewise for pull-switches, roller switches, and similar > methods. Says who? >> As Joe indicates, mercury switches do work...sometimes. They're no >> longer allowed for high-power rockets, partly because of that >> "sometimes." Likewise for pull-switches, roller switches, and similar >> methods. > > Says who? Good to see another of the valued old regulars back! >> As Joe indicates, mercury switches do work...sometimes. They're no >> longer allowed for high-power rockets, partly because of that >> "sometimes." Likewise for pull-switches, roller switches, and similar >> methods. > >Says who? If memory serves...The high-power rocketry safety code. There have been incidents of rockets that launched inadvertently. For example, a roller switch that was intended to tell a circuit when the rocket left the rod, was used on a too-small rod. (That's from memory. I think.) Mercury switches are possibly more of an environmental issue, I dunno. But with the price and capability of today's electronics, there's a dozen more reliable ways to start an upper stage. Terry >> As Joe indicates, mercury switches do work...sometimes. They're no >> longer allowed for high-power rockets, partly because of that >> "sometimes." Likewise for pull-switches, roller switches, and similar >> methods. > > Says who? Mercury switches etc. are not prohibited by the high power safety codes: TRA, NAR, and NFPA. But they are prohibited by the TRA Research Safety Code. http://www.tripoli.org/documents/ResearchSafetyCode_Jan_09_r3.pdf  SignatureDavid W. Schultz http://home.earthlink.net/~david.schultz "Ridicule is the burden of genius." - Plucky Duck > >> As Joe indicates, mercury switches do work...sometimes. They're no > >> longer allowed for high-power rockets, partly because of that [quoted text clipped - 7 lines] > > http://www.tripoli.org/documents/ResearchSafetyCode_Jan_09_r3.pdf This is interesting because the rules state "The ignition of a research rocket motor shall not be initiated by any of the following:"... mercury switches, pull wires, pressure roller switches. This looks to me to be poorly worded. I think one could argue that the motor is "initiated" by the igniter, or the circuit directly attached to the igniter. The mentioned components might not be part of the circuit that directly initiates the motor. Additionally, it states that "a switch that uses mercury to complete a circuit" cannot be used. I can get around that rule by using a mercury switch in a circuit that fires when mercury in the switch BREAKS the circuit. I understand what they are trying to say, I don't know if I fully agree (there should be a SOME way to make exceptions for certain designs, IF they are proven safe/reliable). Anyone want to buy some mercury switches? >This is interesting because the rules state "The ignition of a >research rocket motor shall not be initiated by any of the [quoted text clipped - 10 lines] >for certain designs, IF they are proven safe/reliable). Anyone want >to buy some mercury switches? Sorry about that, folks, I thought it was the high-power safety code. As mentioned elsewhere, it's in the Research code. And it's probably a good idea regardless. Dan, it's indeed possible for me or you to interpret the code in some other way. But how *I* interpret a rocketry safety code matters not one whit. It's how the *underwriter* of the insurance interprets the code. In response to the get-around on mercury switches, a hypothetical insurance investigator would say "Sorry, the switch you used did use mercury to complete a circuit; the fact that the contact was broken to fire the igniter is immaterial. IOW you lose." It's all about the insurance. Best -- Terry "Insurance companies don't make money by *paying* claims, they make money by *not paying* claims." > On Wed, 29 Apr 2009 23:39:01 -0700 (PDT), Dan Major > [quoted text clipped - 14 lines] > "Insurance companies don't make money by *paying* claims, they make > money by *not paying* claims." I wasn't aware insurance reps were at the launches. I've never been to a Tripoly "research launch" so I am speaking from ignorance. I was imagining that it would be similar to out local "sponsored" (ie. NRA/ TRA sanctioned launch) where the RSO was the man with the last word. There have been times when he could be talked into exceptions knowing that it was an experimental system. The exceptions were made with common sense, not a brainless "no tolerance" attitude like we see too much of today. I *still* think it could be better worded. Any one want to buy some mercury switches? > >http://www.tripoli.org/documents/ResearchSafetyCode_Jan_09_r3.pdf > [quoted text clipped - 12 lines] > for certain designs, IF they are proven safe/reliable). Anyone want > to buy some mercury switches? I'm in agreement (although not a research flier...yet). I don't see any of these triggering mechanisms as being any less reliable than a g-switch when used in conjunction with the robustness of a timer like the miniTimer3. For example, bumping into something on the way to the pad, or tripping, could cause a g-switch to close. If the circuitry connected to it fired immediately rather than waiting for a 1/2 second period of sustained closure, then it would be as risky as the mercury switch, or pull wires, etc. The converse is true. If a pull wire or pressure roller switch is used in conjunction with a timer that includes input signal integration as well as a good, safe arming sequence, they are just as reliable as the g-switch based timer mechanism. No? I'm not trying to change the rules, just trying to clarify that it's not the input device that's at fault - it's the overall mechanism employing it that determines what's reliable and hence what's safe. Doug . ... > I'm not trying to change the rules, just trying to clarify that it's > not the input device that's at fault - it's the overall mechanism > employing it that determines what's reliable and hence what's safe. Well, they're trying to legislate by negatives (le: "these shall not be used..."). They need to be more positive in rule making. For example, mandating that a safety device that only allows the staging or recovery system to receive power when it is on the pad, immediately before launch. This is an obvious design feature to me, but might not be to someone else as there have been mentions of accidents on the way to the pad. > ... >> [quoted text clipped - 9 lines] > be to someone else as there have been mentions of accidents on the way > to the pad. Worse, they seem to be trying to legislate in terms of specific technologies, which means you end up with people either trying equally bad (or even worse) technologies that are forbidden, or not trying better technologies that are not approved. The approach you describe, describing required behaviors, is what you want. Note that your approach can be combined with examples of technologies that do and do not meet the standard, so people have guidance in meeting the standard. (on a similar note in a completely off-topic instance of thread drift, I saw recently that California is trying to develop standards for heat transfer in automotive paint -- the idea is to reduce the necessity for air conditioning, to improve gas mileage and reduce greenhouse gas emissions. A much, much better approach would be to limit heat transfer into the interior of the car, so automakers could balance the characteristics of the paint, the glass, and the insulation to meet a real standard). > (on a similar note in a completely off-topic instance of thread drift...(sound of large snippage) The discussion didn't really slide off topic (air starting...). I've been interested for a long time in a Nike-(something) two-stage rocket. I've designed and prototyped several locking/release mechanisms to try and develop either a BP "ducted staging" method where the flaming bits get transfered up to the upper stage and ignite the engine, or an electrical staging timer. The first instance, using BP motors is the most interesting/challanging. I've come up with a couple of ways the whwn the two stages seperate, a "lock" disengages and a spring pushes the parachute out. Doing everything via electronics is (of course) easier, but the development costs are higher (from scratch anyway), so the costs to the customer are higher (unless you sell a metric buttload of them). Along these lines, I'd also like to make a BP-powered MBDA Aster: http://en.wikipedia.org/wiki/MBDA_Aster http://www.naval-technology.com/projects/formidable/formidable6.html http://www.mbda-systems.com/mbda/site/ref/scripts/siteFO_contenu.php?lang=EN&noe u_id=88&page_id=7 >> (on a similar note in a completely off-topic instance of thread drift...(sound of large snippage) > > The discussion didn't really slide off topic (air starting...). It was my bringing up California that was the off-topic thread drift. > I've > been interested for a long time in a Nike-(something) two-stage [quoted text clipped - 9 lines] > higher (from scratch anyway), so the costs to the customer are higher > (unless you sell a metric buttload of them). Good luck! I definitely prefer the black-powder ejection charges, though (disclaimer -- theoretically. I haven't tried a two-stage non-BP, and my only BP two-stages have used normal Estes-style tumble-recovery boosters). > Along these lines, I'd also like to make a BP-powered MBDA Aster: > http://en.wikipedia.org/wiki/MBDA_Aster > http://www.naval-technology.com/projects/formidable/formidable6.html > http://www.mbda-systems.com/mbda/site/ref/scripts/siteFO_contenu.php?lang=EN&noe u_id=88&page_id=7 > Good luck! I definitely prefer the black-powder ejection charges, > though (disclaimer -- theoretically. I haven't tried a two-stage > non-BP, and my only BP two-stages have used normal Estes-style > tumble-recovery boosters). The more I think about it, the more I'm leaning toward the inexpensive miniTimer3 Doug referred to. Normal black powder motor (with delay and ejection charge), recovery system and timer in the booster. Bring the wires for upper stage ignition through the transition (need a connection scheme that reliably withstands liftoff Gs). Launch, timer starts, booster burns out, upper stage lights, delay, booster deploys recovery system, upper stage deploys recovery system. Seems doable. > A much, much better approach would be to limit heat transfer > into the interior of the car, so automakers could balance the > characteristics of the paint, the glass, and the insulation to meet a > real standard). Drifting OT in the finest rmr tradition, I now see in my mind the California solution: All cars will have a tree planted in the trunk which not only provides shade for the car - thereby limiting heatflow into the car - but also converts to O2 some of the CO2 produced by the car :) Doug . > Forgive my naive questions, but (geez, I feel like a newbie all over > again :) ... [quoted text clipped - 5 lines] > 5, 8 or 11). That makes it not-so-tempting. Does anyone know if the > reloads intended for the RMS-24/40 can be used in the 24/60 hardware? No, you cannot use the reloads for the 24/40 in the 24/60. The 24/40 is the 'equivalent size' of the Estes D, the 24/60 is the equivalent size of the Estes E. Further, I'm not sure of the inside diameter of the cases is the same -- if the 24/60 has a thicker wall, then there's no chance at all of using the 24/40 load, even if one were to rig a spacer. > Also, how do the high power folk manage to air start motors? Are > there electronics that can detect booster stage burnout? One of the [quoted text clipped - 5 lines] > > Thanks. There are several 'staging timers' available, which typically trigger off of an acceleration (or other method of ensuring launch), start a timer, and trigger the ignition of the upper stage some specified time later. David Erbas-White > > Forgive my naive questions, but (geez, I feel like a newbie all over > > again :) ... [quoted text clipped - 28 lines] > > David Erbas-White As Gary has said on the much-more-useful "The Rocketry Forum", more reloads are coming. Different loads with different propellants will be introduced in a staggered timeframe. We should be just about due for the second variety. He answers questions on TRF or via e-mail directly on the Aerotech website VERY fast. Of course, if you ask him directly, you will not get to read our "guess" answers to Aerotech business or technical questions. |
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